As the demand for diesel and jet boiling range fuel increases worldwide, there is increasing interest in feedstock sources other than petroleum crude oil. One such source is what has been termed “renewable” and “biological” feedstocks. These renewable biological feedstocks include, but are not limited to, plant oils such as corn, jatropha, camelina, rapeseed, canola, and soybean oil, algal oils, and animal fats such as tallow and fish oils. The common feature of these sources is that they are composed of glycerides and Free Fatty Acids (FFAs). Both of these classes of compounds contain normal aliphatic carbon chains having from about 8 to about 24 carbon atoms. The aliphatic carbon chains in the glycerides or FFAs can be fully saturated or mono, di- or poly-unsaturated. The sidechains of the glycerides and the FFAs in biological oils and fats can be converted into diesel or jet fuel using many different processes, such as hydrodeoxygenation and hydroisomerization processes.
Fuel processed from renewable biological sources is desirable for a variety of reasons. Foremost, the use of renewable biological-sourced fuels reduces the demand for the extraction and use of fossil fuels. This is especially true for transportation fuels such as diesel and jet fuel. In addition to the ecological benefits of using biological-sourced fuel, there exists a market demand for such fuel. For fuel purchasers, the use of biological-sourced fuel can be promoted in public relations. Also, certain governmental policies may require or reward use of biological-sourced fuels.
However, renewable biological feedstocks present challenges in processing. Some renewable feedstocks are high in nitrogen (e.g. low grade animal fats—packer tallows) and therefore more difficult to process in the first stage deoxygenation step. Organic nitrogen conversion to ammonia is a competing reaction to the necessary deoxygenation reaction. These high nitrogen feeds are generally cheaper in the market place. However, processing the cheaper feeds may be more expensive and costly. Thus, they may not represent a real commercial value.
Therefore, there is a need for processes that can effectively and efficiently convert renewable biological feedstocks, especially feedstocks high in nitrogen, into linear hydrocarbons for the production of fuels such as diesel and jet fuel.